F-18 fluorodeoxyglucose (FDG) used with positron emission tomography (PET) has been shown to be very effective for detecting malignant tumors in vivo. It is assumed the increased uptake seen in tumors is due to increased glycolysis, i.e. increased metabolism of glucose to lactate. However, an alternative possibility, based on direct measurements of uptake of glucose and FDG by tumors is that tumors have an increased affinity for FDG. The term "lumped constant" is the ratio of uptake of FDG to that of glucose. It seems to be elevated in tumors. The overall goal of this project is to understand the mechanism for the relative increased uptake of FDG by tumors and to take advantage of this difference by optimizing the analysis methodology and the imaging protocols.